A flow control valve for a construction machine in the prior art, as illustrated in FIG. 1, includes a valve body 5 in which a pump passage 1 through which hydraulic fluid from a hydraulic pump is supplied, a supply passage 2 connected in parallel to the pump passage 1, and actuator ports 3 and 4 connected to hydraulic actuators, such as hydraulic cylinders, are formed; and a spool 7 installed in the valve body 5 and shifted in response to application of pilot signal pressure thereto to make the supply passage 2 and the actuator port 3 or 4 communicate with each other so as to supply the hydraulic fluid from the hydraulic pump to the hydraulic actuator through the one actuator port 3 and simultaneously return the hydraulic fluid that is discharged from the hydraulic actuator to a hydraulic fluid tank through the other actuator port 4 and a tank passage 6.
In the drawing, the unexplained reference numeral “10” denotes a relief valve that returns a part of the hydraulic fluid to the hydraulic fluid tank through the tank passage 6 if pressure of the hydraulic fluid that is supplied to the hydraulic actuator exceeds a set value.
According to the flow control valve in the prior art as configured above, if the pilot signal pressure is applied to the right signal pressure port of the valve body 5 to shift the spool 7 in the left direction in the drawing, the hydraulic fluid from the hydraulic pump passes through the pump passage 1, the supply passage 2, a notch 8 of the spool 7, and the actuator port 3 in order, and then is supplied to the hydraulic actuator to drive the hydraulic actuator.
At the same time, the hydraulic fluid that is discharged from the hydraulic actuator passes through the actuator port 4, a notch 9 of the spool 7, and the tank passage 6 in order, and then is returned to the hydraulic fluid tank.
However, according to the flow control valve in the prior art as described above, in the case of controlling the flow rate so that the hydraulic fluid from the hydraulic pump passes through the pump passage 1, the supply passage 2, and the actuator port 3 in order and then is supplied to the hydraulic actuator through the shifting of the spool 7, the flow rate of the hydraulic fluid, which is supplied to the hydraulic actuator through the notch 8 of the spool 7, may differ depending on the pressure generated in the hydraulic pump and the hydraulic actuator and the change of the supplied flow rate of the hydraulic pump.